Research from the US suggests that exercising or being physically active is linked to a reduced risk of invasive premenopausal breast cancer, and the reduction is even higher when girls and women start regular physical activity in early adolescence and continue into adulthood.
The study is the work of researchers at Washington University School of Medicine in St Louis and Harvard University in Boston, and is published in the 13th May advance access online issue of the Journal of the National Cancer Institute.
There is quite a lot of evidence linking physical activity with lower risk of postmenopausal breast cancer, but the link with invasive premenopausal breast cancer is less clear, despite it representing around 25 per cent of breast cancers and being more aggressive.
For this study, the researchers used data from nearly 65,000 premenopausal women aged between 24 and 42, from across the US taking part in the Nurses’ Health Study II, one of the largest prospective investigations into the risk factors for major chronic diseases in women. The women started reporting their leisure time physical activity from age 12 to their current age in 1997.
The investigators used statistical methods called regression models to find links between risk of invasive premenopausal breast cancer and physical activity in the participant data. The physical activity was categorized by three age ranges: adolescence, adulthood, and lifetime, and four measures of intensity: strenuous, moderate, walking, plus an overall figure.
The results showed that:
- During the 6 years of follow up, 550 premenopausal women were diagnosed with breast cancer.
- The strongest links with elevated risk of premenopausal breast cancer were with total leisure time activity for the lifetime age range rather than with any other exercise intensity and age period.
- Age-adjusted incidence rates for invasive breast cancer dropped from 194 cases per 100,000 person-years in the least active women to 136 cases in the most active.
- Women who exercised for the equivalent of 3.25 hours a week of running, or 13 hours a week of walking, had a 23 per cent lower risk of premenopausal breast cancer compared with women who were less physically active.
- This does not mean the women ran for 3.25 hours a week or walked for 13 hours a week. These figures represent the total metabolic equivalent exercise value of the physical activity the women engaged in during an average week.
- High levels of physical activity from age 12 to 22 contributed the most to the lowered risk effect.
The researchers concluded that:
“Leisure-time physical activity was associated with a reduced risk for premenopausal breast cancer in this cohort. Premenopausal women regularly engaging in high amounts of physical activity during both adolescence and adulthood may derive the most benefit.”
In a prepared statement, issued yesterday, lead researcher Dr Graham Colditz, Niess-Gain Professor and associate director of Prevention and Control at the Siteman Cancer Center at Washington University School of Medicine and Barnes-Jewish Hospital, said:
“We don’t have a lot of prevention strategies for premenopausal breast cancer, but our findings clearly show that physical activity during adolescence and young adulthood can pay off in the long run by reducing a woman’s risk of early breast cancer.”
He said these findings were:
“One more reason to encourage girls and young women to exercise regularly.”
Colditz also explained that, “you don’t have to be a marathon runner to get the risk-reducing benefits of exercise”.
One explanation for why exercise might have such a strong effect on breast cancer risk in younger women, is that being active reduces a woman’s estrogen levels. Higher levels of estrogen have been linked to higher risk of breast cancer.
“A Prospective Study of Age-Specific Physical Activity and Premenopausal Breast Cancer.”
Sonia S. Maruti, Walter C. Willett, Diane Feskanich, Bernard Rosner, and Graham A. Colditz
Journal of the National Cancer Institute Advance Access published on May 13, 2008.
DOI:10.1093/jnci/djn135
Sources: Journal abstract, Washington University press release.
Written by: Catharine Paddock, PhD